A wide variety of artificial spinal disk designs have been developed over the past several years. Some designs, such as those described in U.S. Pat. Nos. 6,001,130 and 5,123,926 include resilient plastic or fluid filled bag type structures that are placed between adjacent vertebra. These designs provide flexibility, but present the risk of rupture or breakage, and can be difficult to contain effectively within the disk space. Other designs have attempted to use ball-and socket type couplers between endplates or other retaining devices attached to the vertebral bodies. Currently, devices which use metal-metal interfaces rather than resilient bodies are favored for their reliability and strength. However, these types of couplings do a poor job of imitating the natural relative movement of vertebral bodies separated by a natural anatomical disk. Furthermore, this type of replacement disk typically focuses all the forces from weight and motion in a single direction and on a very small part of each vertebral body. This can cause excessive stress on the bone in the area where the artificial disk connects to the vertebral body. Improved designs that reduce these problems are needed in the art.